The present invention relates to a secondary air supplying device of an internal combustion engine, and more particularly relates to such a device of an internal combustion engine having a catalytic convertor for purifying exhaust gas provided in an exhaust pipe.
In a conventional secondary air supplying device of an internal combustion engine, secondary air is generally injected into an exhaust port in a cylinder head at the downstream side of an exhaust valve, in other words, at the upstream side of an exhaust manifold. However, in such a conventional secondary air supplying device, there is a disadvantage that, when the secondary air is injected into the exhaust passage during a high speed engine operating condition, where the temperature of the exhaust gas is high, the catalytic convertor is overheated because the secondary air reacts with exhaust gas in the exhaust port and in the exhaust manifold, and the temperature of the exhaust gas is increased further. Particularly, if the engine has an exhaust reactor provided in the exhaust manifold, this disadvantage is more significant, because the reaction of the exhaust gas is promoted even more.
In order to overcome this disadvantage, there has been proposed a secondary air supplying device having a secondary air switching valve, by which the supply route of secondary air is changed so that the secondary air is supplied into the exhaust passage at the upstream side of the catalytic convertor after the engine is warmed, and the catalytic convertor is cooled by the secondary air. However, the secondary air switching valve used in such a secondary air supplying device is operated with vacuum pressure drawn from the intake manifold and, therefore, even after the engine is warmed, when the intake manifold vacuum pressure is reduced to a value lower than a predetermined value, secondary air is again supplied into the exhaust passage at the upstream side of the exhaust manifold. Generally speaking, as an exhaust reactor is provided in the exhaust manifold, the secondary air supplied at the upstream side of the manifold reacts with exhaust gas in the exhaust reactor and its temperature becomes high. As a result, the effect of preventing the catalytic convertor from overheating by the secondary air is not sufficiently attained and the purification effect of the exhaust gas by the catalytic convertor is not sufficiently attained. cl SUMMARY OF THE INVENTION
The principal object of this invention is to provide a secondary air supplying device of an internal combustion engine, in which the supply route of the secondary air is changed so that the secondary air is supplied to an exhaust passage selectively at the upstream side of the exhaust manifold and at the upstream side of the catalytic convertor, and in which the supply route of the secondary air is effectively changed in accordance with the engine operating conditions, the overheating of the catalytic convertor is prevented and the effect of purification of exhaust gas by the catalytic convertor is improved.
According to the present invention, there is provided a secondary air supplying device of an internal combustion engine having an exhaust passage provided with a catalyzer for purifying exhaust gas passing therein, comprising: first air injection means having a first air injection port provided in said exhaust passage at the upstream side of an exhaust manifold of the engine; second air injection means having a second injection port provided in said exhaust passage at the upstream side of said catalyzer; an air pump for supplying secondary air; a first air changing means connected to said air pump and being adapted to release secondary air to the atmosphere when the engine is in a cooled operating condition and to supply secondary air to a second air changing means when the engine is in warming and warmed up operating conditions, and; said second air changing means being connected to said first air changing means and being adapted to selectively supply secondary air to one of said first and second air injection ports. Said second air changing means comprises an air switching valve constructed as a pneumatic valve having a diaphragm chamber, and said air changing valve supplies secondary air to the first air injection port when atmospheric air is introduced into said diaphragm chamber and supplies secondary air to the second air injection port when the vacuum pressure is introduced into said diaphragm chamber.
The diaphragm chamber of the secondary air switching valve may be communicated with the intake manifold by means of a first vacuum pressure passage and a second vaccum pressure passage positioned in parallel to each other. The first vacuum pressure passage is provided with a pressure delay valve and a vacuum pressure changing switch which is actuated in accordance with the temperature of engine cooling water. On the other hand, the second vacuum pressure passage is provided with a vacuum pressure introduction valve. During a warming operation of the engine, atmospheric pressure is transmitted to the diaphragm chamber from said vacuum pressure changing switch through the pressure delay valve, except that, when the intake manifold vacuum pressure is abruptly increased, such as when the engine is in an abrupt decelerating operating condition, the vacuum pressure is transmitted to the diaphragm chamber through said vacuum pressure introduction valve. On the other hand, after the engine is warmed up, the intake manifold vacuum pressure is transmitted to the diaphragm chamber through the pressure delay valve. However, during a predetermined time interval after the manifold vacuum pressure is abruptly reduced when the engine is in high load operating condition, the vacuum pressure is maintained in the diaphragm chamber.